1. Field of the Invention
The invention relates and pertains to tapping attachments, i.e. tools which carry taps for threading holes and are driven by a driving machine or power center and to reduction of stress and wear for components thereof.
2. Description of the Prior Art
The field of the invention and the prior art are exemplified in the field of self-reversing tapping attachments by reference to prior patents assigned to the assignee of the instant application. These include: U.S. Pat. Nos. 3,999,642; 4,014,421; 4,566,829; 4,705,437; 5,203,651; 5,209,616; 5,213,413 and 5,628,593 and patents cited therein, all of which are hereby incorporated by reference herein. The aforesaid patents and application disclose and claim tapping attachments including a tap holding spindle and simultaneously rotating forward and reverse drivers, the spindle being freely floating and moveable axially with respect to the forward and reverse drivers. Under forward drive in which the tap holder spindle is driven by the forward driver, the tap threads a hole being tapped in the workpiece and thereby screws itself into the hole. Upon cessation of feed by the driving machine with retraction of the driving machine, relative axial movement results between the tap holding spindle and the driver members such that the forward drive member becomes disengaged from the tap spindle which at this point is held relatively stationary due to the fact that the tap has become fastened to the workpiece. Upon further retractive movement by the tapping machine and further relative movement, the reverse drive member becomes engaged with the tap holding spindle, causing reverse rotation thereof and thereby unscrewing the tap from the hole. In this manner, self-reversing by the tapping attachment itself as opposed to reversing by the driving machine, is accomplished. With the advent of powerful Computer Numeric Control (CNC) machining centers, self-reversing has become of greater and greater importance in that it causes reversing to occur in the tapping attachment, as opposed to requiring the driving machine to reverse its direction of rotation.
Self-reversing tapping attachments have particular parts which due to the very nature of self-reversing suffer greater stress and wear than other parts, especially in connection with modern ultra-high-speed tapping. Such stress and wear occur primarily in the transition between forward and reverse, wherein the balls in the coupling on the tap holding spindle proceed through a limited neutral zone between engagement with splines on the forward drive element and splines on the reverse drive element.
Existing devices such as those described and claimed in the above-described patents and patent application have improved stress resistance and useful life of wearable components; however, ever higher demands of speed and performance call for further improvement in wearability and reduction of stress on wearable parts.
Thus, there has been a need for further improvements in decrease of wear and reduction of stress on wearable parts in tapping attachments, particularly with respect to those operable at ultra-high rpm.